The present invention relates to the extrusion of honeycomb bodies from plastic batches, and more particularly to an honeycomb extrusion apparatus having an improved control system for batch flowing into an skin-forming region of the die.
In an extruder, the batch flow path in the peripheral areas of the die, where the skin of the honeycomb structure is formed, is more complicated and more difficult to control than in the main field of extrusion, where the body of the honeycomb structure is formed. Batch flow control in the peripheral area of the die is important because skin defects (i.e., air checks, cell distortion/deformation, blisters, and the like) can later result in product failure.
U.S. Pat. No. 4,710,123 (Ziebig et al.) discloses an apparatus with adjustable means on the outlet side of the die for regulating the flow of the batch in the skin region, and bringing it in conformity with the flow rate of the batch in the main body region. The apparatus can also include a device (i.e., breaker plate) positioned at the inlet side of the die for further batch flow control.
U.S. Pat. App. Pub. 2003/0001308 (Shibagaki et al.) discloses an apparatus for controlling the batch in the skin region, the apparatus having an adjusting instrument with a flexible part which can be lowered into the skin region to regulate the flow rate.
Although these references address the problem of correlating flow between the skin and body regions, they provide no solution to the observed problem that flow rate differences in the material batch between the skin and body regions vary with die location. A disadvantage of the previous apparatuses is the allowance of only uniform correction of skin-body flow rate difference around the die. Under such circumstances skin-body flow rate differences may be insufficiently corrected at some locations around the die.
Therefore there exists a need for an extrusion apparatus which can satisfactorily adjust differences in skin-body flow rates at multiple locations around the die. Furthermore, there also exists a need for an extrusion apparatus which allows for the external manipulation of the interior components controlling batch flow, during the production without having to stop manufacturing operations to effect the necessary changes thereat.